1. Field of the Invention
The present invention relates to an Fe--Cr alloy, exhibiting excellent ridging resistance, corrosion resistance and workability, for steel sheet having excellent surface characteristics.
2. Description of the Related Art
Fe--Cr alloys, such as ferrite stainless steels, having excellent characteristics, e.g. high corrosion resistance and thermal resistance, are widely used in various industrial fields, such as household articles and automobile parts. Because such alloys, however, have drawbacks in workability, and in detail, ridging, in other words, a surface defect like rough dry skin readily forms during press working of the thin steel plate, for example, such alloys are not suitable for the usage in which heavy working, such as deep drawing, are applied.
Many attempts have been proposed to solve the drawbacks set forth above. For example, Japanese Unexamined Patent Publication No. 52-24913 discloses the improvement in ridging resistance by a specified composition, i.e., a ferrite stainless steel exhibiting excellent workability which comprises 0.03 to 0.08% by weight of C (hereinafter "% by weight" is expressed as merely "%"), 0.01% or less of N, 0.008% or less of S, 0.03% or less of P, 0.4% or less of Si, 0.5% or less of Mn, 0.3% or less of Ni, 15 to 20% of Cr, 2.times.N to 0.2% of Al, and the balance Fe and inevitable impurities. Further, Japanese Unexamined Patent Publication No. 7-18385 discloses an Fe--Cr alloy exhibiting excellent ridging resistance which comprises 3 to 60% of Cr, decreased amounts of C, S and O, 0.003 to 0.5% of N, and the balance Fe and inevitable impurities. In such prior art, although the ridging resistance is improved by specifying the components, characteristics other than the ridging resistance are unsatisfactory.
Additionally, Japanese Unexamined Patent Publication No. 55-141522 discloses a method for making a ferrite stainless steel with decreased ridging by performing hot rolling in which the slab heating temperature is limited to the range of 950.degree. to 1,100.degree. C. Although the prior art intends to decrease ridging by fining crystal grains at a lower slab heating temperature, defects at the steel surface significantly increase since the heating temperature is lower than the rolling temperature.
In the prior art, although ridging resistance has been improved to some extent as set forth above, such an improvement is not satisfactory in practical uses. Further, no material exhibiting excellent characteristics, e.g. workability, such as elongation and r value, and surface characteristics, such as corrosion resistance and packed scab, has been proposed.